1. Field of the Invention
The present invention relates to a call controlling apparatus and method used for an order-wire system which helps improve reliability and maintainability of a communication system.
In wire and radio transmission systems using the SDH (Synchronous Digital Hierarchy) transmission method, for example, a communication channel for the order-wire system is provided between terminal equipment for exchanging maintenance information and so on, through the channel, in order for maintenance personnel to mutually exchange maintenance information, for example. The communication-channel information is transmitted multiplexed with user information or a payload.
There are two types of channels for the order-wire system: a channel available only between tributary offices and that available between a terminal office and an intermediate repeater station of the communication network. Those channels are specified in E1 and E2 bytes respectively in the SDH transmission frame (hereinafter the channels via the E1 and E2 bytes are called E1 and E2 channels, respectively).
There have been practiced two ways of calling the other end by using the order-wire system: a way to use an oral sound and the other to give an audible signal such as a ringing tone which is sounded by sending a dual tone multiple frequency (abbreviated to DTMF) signal. The present invention relates to the latter way of the order-wire system. Accordingly, a call controlling device which is high in reliability of the device and high in maintainability of the communication system is in great demand.
2. Description of the Related Art
FIG. 1 shows a network system which the present invention is applied to. The network system includes terminal equipment 70 provided between wire transmission lines and terminal equipment 80 provided between wire and radio transmission lines. For easy understanding of the order-wire system, the terminal equipment are simplified and intermediate repeater stations which are provided between terminal equipment, are omitted in FIG. 1.
The terminal equipment using the SDH transmission method, for example, is comprised of transceivers (XCVR) 71/75 and 81/85 corresponding to up/down lines, for transmitting and receiving a transmission signal; data controllers (DCONT) 72/74 and 82/84 corresponding to up/down lines, for extracting and inserting E1- and E2-byte signals from and in the transmission signal; and order-wire controllers (abbreviated to ORDW CONT) 73, 83 for controlling the order-wire system.
The order-wire system is equipped with first and second telephones for communicating respectively via the E1- and E2-byte signals (hereinafter may called E1 and E2 channels). It extracts the E1- and E2-byte signals from the transmission signal and decodes the signals to reproduce sound and voice on the telephones. It also encodes sound and voice generated from the telephones into E1- and E2-byte signals and inserts the signals in the transmission signal.
Prior to communication via voice, a calling party sends out the E1-byte signal, for example, into which the phone number of the first telephone is encoded, with the signal inserted in the transmission signal. In a called party, the E1-byte signal is extracted from the received transmission signal and encoded into a DTMF signal, for example, which in turn is decoded into a phone number. When the phone number is detected as belonging to one of the first and second telephones, a call is made on the telephone by sounding a ringing tone.
In a call controlling device of the related art, using the DTMF signal, for example, there were two methods of controlling a call:
The first method had two sets each of a telephone for receiving a call, a DTMF decoder for decoding a DTMF signal into a digital phone-number signal and a call controller for making a call on the telephone based on the phone-number signal, each set corresponding respectively to the E1 and E2 channels. Thus, the E1- and E2-byte signals were respectively input to the DTMF decoder and each set detected and controlled a call directed to the first and second telephones independently.
The second method had a single set of a telephone, a DTMF decoder and a call controller. The E1- and E2-byte signals were selectively input to the DTMF decoder by using a manual switch to detect and control a call to the telephone.
It is a problem of the related art that the call controlling device of the first method is large-sized and costly and decreases in reliability of the device because it requires large amount of circuitry including two separate sets of the circuits. It is another problem of the related art that the call controlling device of the second method decreases in maintainability of the system because it involves a manual switching operation, preventing maintenance personnel from communicating immediately as occasion demands.